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Reply #46: It's not your firefox or IE that's failing to work [View All]

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DisgustipatedinCA Donating Member (1000+ posts) Send PM | Profile | Ignore Mon Feb-28-11 10:27 PM
Response to Reply #43
46. It's not your firefox or IE that's failing to work
It's the underlying DNS that they depend on. Goes something like this:

-you put democraticunderground.com in your browser and hit go.
-your pc does a "DNS lookup". It goes to a DNS server and sez, hey, what's the IP address for www.democraticunderground.com ?
-your pc sends the "DNS lookup" request to its configured DNS servers. This is usually done automatically by ISP's for home users.
-the DNS servers that your PC goes to looks around, and says, I don't have that IP address.
-that DNS server then goes and asks other DNS servers on the internet, hey, who has the IP address for DU? This person wants to browse there.
-the other DNS servers don't know. The request eventually gets to the Big Boss of DU DNS, the "authoritative nameserver". In this case, it's called "ns1.dca.net". If the server ns1.dca.net decides Democraticunderground is the IP address 4.5.6.7, everyone else has to listen. This server is The Decider. (no, 4.5.6.7 is definitely not the IP address for DU, but this just points out that misconfigurations can and do happen, usually off by just a digit :) ).

-When The Decider (ns1.dca.net) sends out a change regarding DU's DNS (this could be due to the server moving to a different IP address or even a domain accidentally being deleted), this server talks to all its DNS server pals and tells them about the change. Along with this message is something called a TTL, or time to live. If the TTL is set very low (say 60 seconds), then all of the other DNS servers out there should get the new and corrected info about DU DNS in short order.

-BUT, other DNS servers don't always play nice, and they don't always "honor" ttl's. They'll get notification of DNS changes for DU, but they'll wait until 2AM local time to propagate those changes and other changes that have come in from other websites over the course of a day.

-Result: a slow-motion train wreck. The original failure (whatever its nature) didn't hit my local ISP until 7 or so this evening, although the problem has been going on for hours. The actual fix may take up to another day (but probably not that long, in most places). So the fix spreads out all across the Internet at different rates, just like the failure spread. There is no quick and complete fix.

-a note about Anycast. You've seen people here recommending going to Google's public dns servers at 8.8.8.8, etc. This works for some, not for others. But each IP address is individual, and only goes to one server, so everyone should be able to get to it barring big Internet routing problems, right? Not quite. Large companies like Google need to be very resilliant, always up. So the address 8.8.8.8, which belongs to Google, actually goes to a great many servers all over the world. If you configure your DNS for 8.8.8.8, it will go to the "nearest" version of the 8.8.8.8 server (as determined by a routing protocol called bgp). That way, if there's an earthquake in CA or a big undersea trunk that's been cut, there will always be an "8.8.8.8" address you can get to. This is called Anycast. It's a really cool thing, but I think it's leading to confusion in this case. I don't think Google's DNS has fully propagated yet, so some people can get to DU using the Google DNS servers, but some cannot.

The good news is that this will all be fixed; it just may take some time.
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